Field of the Invention
The present invention relates to a rubber composition excellent in workability. This rubber composition is useful as a raw material for a vulcanized rubber for tires that is excellent in rigidity and wet performance.
Description of the Related Art
Tires are generally used in various running environments, and are required to be improved in wet performance, which is gripping performance on a wet road surface, for example, in rain. When a blend design for a rubber composition is made to improve this wet performance, the resultant vulcanized rubber may be lowered in rigidity so that a tire of the rubber may be deteriorated, for example, in steering stability. In short, the wet performance and the rigidity of tires are contradictorily related to each other, and it has been therefore required to develop a technique for improving these properties with a good balance.
In order to attain compatibility between low exothermicity and high modulus of a pneumatic tire, Patent Document 1 listed below describes a technique of blending an acid-modified polyolefin and a polyolefin into a rubber composition including a diene rubber.
In order to improve the workability of a rubber composition which is a raw material for pneumatic tires, Patent Document 2 listed below describes a technique of blending, into a rubber composition, an acid-modified polyolefin having a melt mass flow rate of 100 q/10-min., or more.
In order to improve a pneumatic tire in wet gripping performance and in steering stability under high-temperature conditions with a good balance, Patent Document 3 listed below describes a technique of blending, into a rubber composition, silica and a crystalline higher-α-olefin copolymer having a melting point of 60° C. or lower.
Furthermore, in order to improve a vulcanized rubber in tear strength, Patent Document 4 listed below describes a technique of blending a polyolefin copolymer or polypropylene into a rubber composition, which is a raw material for the vulcanized rubber.